1. Field of the Invention
The present invention relates generally to a secondary battery, a display method, a recording medium and a program, more specifically to a method, a recording medium and a program to let the user know or recognize the residual capacity of a secondary battery.
2. Description of Related Art
There are batteries to be installed in a video camera or the like for supplying operating electrical power to a device (or an equipment) in which the batteries are installed. Improved performance of such batteries enables a user to extend the operating time of such device. The batteries can be classified into a primary battery which can be used only once until its electrical capacity is consumed, and a secondary battery which is repeatedly usable by connecting to a dedicated charger when its electrical capacity is consumed depending on the number of their usage. In other words, the secondary battery is the battery which is reusable for many times by repeatedly recharging it.
Among such secondary batteries, there exists a secondary battery which is equipped with a display or an indicator for indicating its residual capacity so that a user can recognize the proper timing for charging, for example. (See, for example, Japanese Patent No.3225580, Japanese Non-examined Patent Publication No.5-283110, and Japanese Non-examined Patent Publication No.9-167638).
In order to indicate for the user to recognize the residual capacity of a secondary battery, it is necessary to judge the residual capacity. One typical method of judging the residual capacity is to monitor the voltage change of the secondary battery. However, a method of simply monitoring the voltage change encounters a problem that it is hard to judge accurate residual capacity.
Now, such problem will be described in detail with reference to FIG. 1 which shows a graph of the residual capacity or the voltage of a secondary battery in the vertical axis as a function of time in the horizontal axis. As the time passes, the residual capacity of an actual secondary battery decreases like a linear function as shown by a line A. The voltage of the secondary battery decreases gradually at the initial stage, but decreases sharply after elapsing a certain time as shown by a line B, which is not a linear function.
As described hereinabove, since the voltage of a secondary battery which is the original data for the display for a user to identify the residual capacity of the secondary battery does not change like a linear function, the electrical capacity of the secondary battery to be calculated based on the voltage becomes as shown by a line C. In other words, the line C indicating the residual capacity to be calculated based on the voltage change of the line B becomes also a line that decreases sharply after elapsing a certain time similar to the line B. A numerical difference between the line A and the line C results in an error between the actual residual capacity and the residual capacity calculated by the voltage. As shown in FIG. 1, an encountered problem is that the error is very large and thus information which is provided to the user as the residual capacity is rough and is not necessarily accurate.
Even if provided the information which is not necessarily accurate to the user, the user can utilize such information to make a decision of the timing when the secondary battery is to be charged. In other words, the user feels a good usability to the secondary battery having such means to give the residual capacity as compared to a secondary battery having no such means. This is the reason why a secondary battery provided with such means is increasingly preferred in the marketplace.
By the way, there are, for example, audio or visual means to let the user recognize the residual capacity. As a display for a user to recognize the residual capacity, it is preferable to provide more accurate information in a manner easily understood by the user, and thus improving usability. For this end, it is preferable that the user is able to try the indication or display of the residual capacity when he/she is going to buy such secondary battery.
However, an encountered problem is that it is difficult for a user to check the way of displaying the usability (or the display function) when the user buys such secondary battery, i.e., when it is exhibited in a shop.
Additionally, even if the display function can be checked while a secondary battery is exhibited in a shop, there is a problem that the user can check only one display mode at the instance when the user is checking. That is, the user can check only one condition among various display conditions, for example, either condition when the secondary battery is fully charged or it is empty even if the each condition has different display mode, respectively.
The reason is that the residual capacity of a secondary battery does not substantially change while it is in a shop, thereby always providing the same display while checking a secondary battery. As a result, even if a secondary battery is provided with improved display functions, it is impossible to sufficiently demonstrate or appeal such features in a shop.